Rotary contact seals are seals in which the rotating and stationary seal faces are kept in nominal contact. The seals have minimum fluid leakage but are limited in speed capability by frictional heat generation and wear problems at the interface between the faces. Rotary contact seals can be either circumferential seals, with a circumferential contact area between the internal diameter of a sealing ring and the shaft surface, or face seals with contact between the radial seal faces.
Generally, the basic face contact seal consists of two solid rings of material held in nominal contact along a radial face by an axial load. Usually one of its rings is a soft material such as a carbonaceous material, i.e., carbon and the other would be a hard material such as a metal or metal alloy; i.e., steel, tungsten carbide or silicon carbide. Which ring rotates and which is held stationary depends on the individual seal design and application, although it is more common for the hard ring to rotate. The rotating ring is usually mounted in a fixed position on a shaft, with the stator ring loaded so as to press axially against it. The axial load can be provided by springs, bellows, magnetic means or the like. Although contact seals have negligible leakage characteristics, they are subject to wear problems due to the frictional contact of the surfaces.
Copending U.S. patent application Ser. No. 07/599,482 filed Oct. 10, 1990 now U.S. Pat. No. 5,137,422, discloses an erosion resistant coating for turbo machine gas path components which comprises the thermal spray depositing of a chromium carbide and an age hardenable nickel base alloy onto the surface of the gas path components and then preferably heat treating the gas path component. This reference is incorporated herein as if it were recited in its entirety.
The chromium carbide base thermal spray coating family has been in use for many years to provide sliding and impact wear resistance at elevated temperatures. The most frequently used system by far is the chromium carbide plus nickel chromium composite. The nickel chromium (usually Ni -20 Cr) constituent of the coating has ranged from about 10 to about 35 weight percent. These coatings have been produced using all types of thermal spray processes including plasma spray deposition as well as detonation gun deposition. The powder used for thermal spray deposition is usually a simple mechanical blend of the two components. While the chromium carbide component of the powder is usually Cr.sub.3 C.sub.2, the as-deposited coatings typically contain a preponderance of Cr.sub.7 C.sub.3 along with lesser amounts of Cr.sub.3 C.sub.2 and Cr.sub.23 C.sub.6. The difference between the powder composition and the as-deposited coating is due to the oxidation of the Cr.sub.3 C.sub.2 with consequent loss of carbon. Oxidation may occur in detonation gun deposition as a result of oxygen or carbon dioxide in the detonation gases, while oxidation in plasma spraying occurs as a result of inspiration of air into the plasma stream. Those coatings with a relatively high volume fraction of the metallic component have been used for self-mating wear resistance in gas turbine components at elevated temperatures. These coatings, because of the high metallic content, have good impact as well as fretting wear and oxidation resistance. At lower temperatures, coatings with nominally 20 weight percent nickel-chromium have been used for wear against carbon and carbon graphite in mechanical seals, and for wear in general in adhesive and abrasive applications. These coatings are most frequently produced by thermal spraying. In this family of coating processes, the coating material, usually in the form of powder, is heated to near its melting point, accelerated to a high velocity, and impinged upon the surface to be coated. The particles strike the surface and flow laterally to form thin lenticular particles, frequently called splats, which randomly interleaf and overlap to form the coating. The family of thermal spray coatings includes detonation gun deposition, oxy-fuel flame spraying, high velocity oxy-fuel deposition, and plasma spray.
It is an object of the present invention to provide a coating having excellent contact wear resistance for a contact surface of a face contact fluid seal.
It is another object of the present invention to provide a face contact fluid seal in which one of the contacting surfaces is coated with a chromium carbide-age hardenable nickel base alloy coating that has excellent contact wear characteristics.
It is another object of the present invention to provide a method for coating a contact surface of a face contact fluid seal with a chromium carbide-age hardenable nickel base alloy coating.
The foregoing and additional objects will become more apparent from the description and disclosure hereinafter set forth.